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I can't resist a clarification to the following excerpt, radiated by
<<<< begin excerpt >>>>>
From: a6561TB@gnn.com (Igor Kessel)
Date: Fri, 13 Sep 1996 01:01:54
Subject: Re: Radio S**t CB stuff
>... the position of the antenna is just about the
>most important factor. The best spot would be in the center of the
>since the area surrounding the antenna is used as well.
> So, in the middle,the whole car would be used as an antenna,
> helping to pick up signals.
Sorry, no. A car is a ground. Antenna is well insulated from it. Its
the high position, unobscured the by the car's sheet metall, which
acts as a shield, that's what counts. That is why same ant works bad
on the trunk.
>>>>> end of excerpt <<<<<
Well, the obscuration of the trunk location by the roof is a valid
construct, but, if I recall my electromagnetic theory of 30+ years
ago, the metal car roof has a much more important effect than being a
ground. The conductive roof acts as a ground plane, in effect a
mirror to the wave, and by reciprocity, to the antenna pattern. This
makes the quarter-wave whip into a half-wave vertical dipole. I have
forgotten the impact of this, but I suspect that an infinite ground
plane provides a 3 dB (factor of 2) improvement over the whip antenna
alone suspended in space (far above the ground). At CB frequencies,
the wavelength is larger than the car, but the conductive earth is
within a wavelength, so the gain is probably closer to 2 than to 1.
Mandatory word: QUATTRO
*** ...Kirby (Kirby A. Smith) ***
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